Water beetles constitute an ecologically and morphologically most diverse group
of aquatic macro-organisms. They occur in almost every type of inland water
world-wide. Most species are very small in size and usually lead a secluded
life in swamps, rivers, and the like. However, the largest representatives,
which often are encountered in paddies and rural ponds reach almost five centimeters
in length.

While the smaller species feed mainly on microscopic algae, some of the largest
ones are known to prey on vertebrates including fish. Many species are grey
or brown, but others are vividly colored and some are even as beautiful as gemstones.
Many species regularly need to come to the surface for breathing, but some of
the tiny ones, which dwell in well-oxygenated mountain streams, remain submerged
under water for their whole lives.

Among scientists, aquatic coleopteran lately have received much attention due
to their excellent suitability as bioindicators. Presence or absence of certain
water beetle species is an important factor determining the environmental quality
of rivers and other types of aquatic habitats.